The fat content in cream may be controlled automatically during the separation process or via direct in-line standardization. During automatic separation, the volume of cream discharged from the separator is controlled by a throttling valve that is located at the cream outlet. Progressively larger amounts of cream, with a successively diminishing fat content, are discharged from the cream outlet when the valve is gradually opened. Changes in the cream discharge are matched by equal and opposite alterations in the skim milk discharge. In modern processing plants with diverse products, direct in-line standardization is usually combined with separation. Control valves, flow and density meters, and a computerized control loop are used to adjust the fat content of milk and cream to desired levels (1).
Most commonly, whole milk is preheated to 55-65°C in the regeneration section of the high-temperature short-time (HTST) pasteurizer prior to separation. Following separation, the cream is standardized to a preset fat level, and the fraction intended for standardization of milk is routed and remixed with the proper amount of skim milk to attain the desired fat content. The surplus cream is directed to a separate cream pasteurizer, while the standardized milk flows through the pasteurizer. A typical processing line may be set up much like what is shown in Fig. 2.
Pressure must be strictly controlled in order to enable accurate standardization. This is achieved with a constant-pressure valve located just before the skim milk outlet. The cream-regulating system maintains constant fat content in the cream discharged from the separator by adjusting the outlet flow of cream, regardless of variations in the throughput or in the fat content of the incoming whole milk. A ratio controller mixes cream of constant fat content with skim milk in proportions that result in standardized milk of a specified target fat content (1).
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